The basic processing scheme of a personal computer does not directly facilitate display of visual images showing continuous motion, as particularly exemplified by standard television transmissions. Processing and displaying pictures at this real time rate involves handling a relatively large data stream.
It can readily be seen there are numerous potential uses for the capability of viewing a motion picture or TV type image on an inset portion of a PC screen. In addition to merely watching television, surveillance and security systems come to mind-comparing a closed-circuit view or a person with file copies of photographs and clearance or authorization, for example. Viewing of testing operations (e.g.: wind tunnels or displays of changing data such as oscillographs monitored by remote cameras) while reviewing or correcting calculated data is another possibility. Reviewing forensic simulations on magnetic tape recordings while preparing or reviewing commentary or testimony is another, as well as comparison of still file photographs therewith. Other applications are not difficult to conceive.
Visual images for display on a PC are made up of pixels, or discrete image elements, each pixel requiring an eight bit word for definition. It can be seen that the operating speed of a PC will determine whether or not it is possible to achieve motion display with the smoothness which is characteristic of the standard thirty frame per second real time rate. When the PC lacks sufficient speed to display real time motion, edited or intermittent motion display could still be very useful in many applications.
Prior art methods transmit only one pixel of video at a time on the computer's internal bus, resulting in a transmission time of as much as one second or more for a black and white image, considerably longer for color, which is clearly inadequate for smooth display of images involving motion.
Prior art devices for achieving display of moving images on a PC screen from analog sources have customarily provided extra processing capability to bypass the internal computer bus cycle processing or reduce the machine time required for the picture display. This results in an increase in equipment expense, as processors are relatively expensive, as well as increasing the bulk and installation complexity of the equipment.
Applicant is aware of two current art products which seek to achieve a result similar to the current invention.
1. A device called the MassMicro, selling for about $3,000, it is believed. This device requires two plug-in cards and includes its own video output card, producing a video overlay which it mixes directly with the picture displayed by the PC. The host PC's main processor never sees the data being processed by the MassMicro.
2. A device called the OrangeMicro, selling for about $4,000, it is believed. This device also requires two plug-in cards, and has its own processor, taking over the PC data bus as a bus master processor, so again the PC main processor never sees the data being handled by this device.
In addition to their expense, their requirement for two expansion slots in the PC, and their interference with control by the host PC, neither of these devices is capable of the data delivery speed necessary for smooth motion display on the PC screen.
The current invention provides, on a single plug-in video card at a much lower cost than either of the above-mentioned devices, smooth video motion at up to thirty frames per second. The current invention not only provides, by its novel data transfer stage, picture data at a much higher rate than either of the above devices, but does so under the master control of the host PC, rather than overriding its processing, as do the two devices mentioned above.